The ability to determine the acidity of airborne matter is very important. The presence of certain acidic compounds in the air, such as sulfuric acid, can have adverse health effects. In addition, the measure of aerosol acidity has important implications for public health and workplace conditions. For example, research has shown that there may be a strong correlation between aerosol hydronium concentration and many problems associated with air pollution. The detection of acidic pollutants is also very critical in the many working environments such as the mining industry, fertilizer manufacturing, air plumes from waste landfills, coal power plants, petroleum refineries, and offices located in polluted city areas.
Additionally, accurate measurements of the acidity of the air can help in a wide range of other experiments and studies. For example, studies on secondary organic aerosols (SOAs) are largely dependent on measuring the acidity of airborne particulate matter over time.
In general, ambient particulate matter consists of inorganic and organic constituents. The inorganic matter can include sulfates, ammonium, nitrates, sea salts, crusts, and metal oxides. The organic species consists of elemental carbon and organic carbon. A significant class of organic carbon present in ambient particulate matter is secondary organic aerosol (SOA), which can make up about 20% to about 90% of the ambient organic carbon, depending on location and season.
Currently, evaluation of the effects of particle acidity on ambient SOA is limited by existing analytical methods using a pH meter or ion chromatography (EPA Method IO-4.2. Determination of the strong acidity of atmospheric fine-particles (<2.5 micrometer), U.S. EPA, Center for Environmental Research Information, Office of Research and Development, 1999). Such existing methods focus on measurement of major inorganic ions such as sulfate, nitrate, and ammonium with the assumption that the consumption of inorganic acids is dominated by ammonia titration. Additionally, these existing methods require water extraction and are inefficient for monitoring changes in aerosol acidity over short periods of time since measurement of the acidity is not a short process.
Furthermore, existing methods for measuring acidity of airborne particulate matter may be inaccurate in many cases. For example, such methods may incorrectly estimate proton concentration in aerosol by neglecting the formation of organic sulfates in SOA.
Thus, there exists a need in the art for an improved device and method of measuring the acidity of airborne matter.